1. Field of the Invention
The present invention relates to an element for a belt for use in a continuously variable transmission and a method of blanking such an element out of a metal sheet.
2. Description of the Related Art
Elements for belts for use in continuously variable transmissions (CVTS) comprise a body having V-shaped surfaces for contact with CVT pulleys and a head joined to an upper edge of the body. The head has a pair of ears projecting laterally away from each other in confronting relation to the upper edge of the body. The ears positioned on the opposite sides of the neck and the body jointly define a pair of recesses therebetween. The body has a thin region in its substantially half lower portion whose thickness is progressively reduced toward a lower edge thereof. A plurality of such elements are transversely stacked in an annular shape and bound together by a pair of endless rings in the form of metal webs that are disposed in the recesses, respectively, thus making up a belt. With the elements put together in annular form, the bodies thereof are positioned on the inner circumferential side of the belt and the heads thereof are positioned on the outer circumferential side of the belt.
An element of the type described above is blanked out of an elongate metal sheet by pressing a punch against the metal sheet that is placed on the die of a press. When the punch is pressed against the metal sheet, a counterpunch is simultaneously held against the reverse side of the metal sheet to press the substantially half lower portion of the body into a thin region having a desired cross-sectional shape. Several hundreds of blanked elements are stacked together into an annular shape, and endless rings are inserted into the recesses in the elements, thereby making up a belt for use in continuously variable transmissions.
When such a belt is trained around a pair of pulleys of a continuously variable transmission and turned around the pulleys, it is preferable that the elements be held more closely together at their bodies than at their heads while traveling in an arcuate path around the pulleys and be held in a linearly stacked state while traveling in a path between the pulleys. In order to allow the elements to move smoothly along the arcuate path along the pulleys, the thin region of each of the elements is formed to a nicety by the counterpunch at the time of blanking the element.
When the substantially half lower portion of the body is pressed into the thin region by the counterpunch, however, an excess amount of metal is forced to flow from the lower portion into the upper portion of the body, thereby enlarging the upper portion of the body and hence increasing the thickness thereof. If the thickness of the upper portion of the body is increased until it becomes greater than the thickness of the head including the ears, then the body becomes thicker than the head. With the body being thicker than the head, the elements tend to be held more closely together at their heads than at their bodies while traveling in the path between the pulleys, and are difficult to be kept in a linearly stacked state between the pulleys. As a result, the belt which is traveling between the pulleys is liable to be twisted, and fails to transmit stable power in the continuously variable transmission. In addition, the endless rings in the recesses are likely to be forced into contact with the lower edges of the ears, damaging the elements and the endless rings themselves.